The FemtoFiber Terahertz Freeze enables generation of terahertz radiation inside a cryostat in low-temperature experiments. This way it supports terahertz spectroscopy at ultra-low temperatures. Generating the terahertz radiation in close proximity to the sample prevents distortions of the terahertz beam from any distortions induced by transmission windows or waveguides. This guarantees highest resolution and best experimental results in time- and frequency domain.

The unit consists of an erbium-based 30 MHz oscillator and a consecutive fiber amplifier. The generated pulses are recompressed to a transform-limit of 50 fs. The second-harmonic stage converts the laser pulses to 780 nm, which are ideally suited to seed the THz antennas. The included AOM provides the possibility for fast modulation of the pulse intensities and fast blanking.

A tunable grating compressor compensates temperature induced dispersion gradients within the optical fibers inside the cryostat, carrying the pulse to the THz antennas. After an included reliable and robust fiber-coupling unit, the pulses are into two pathways. One of them can be delayed up to 500 ps with respect to the other arm. The final unit provides two software controlled fiber outputs (780 nm, < 300 fs, 8 mW) in a robust housing.